Confused on which rear end to replace 7.5 with

[david lehman]

I AM BUILDING A 85 ELCO & HAS BEEN MANY YEAS SINCE I HAVE WRENCHED ON CARS
I HAVE BEEN READIND THE THREADS ON REAR END REPLACMENTS,
MOTOR GOING IN IS A 383 STROKER APPROX 520 HP NOW THE REAR END THAT CAME WITH CAR IS A 7.5 10 BOLT 343 POSI LOCKER AFTER READING THREADS IM CON VINCED I NEED A STRONGER REAR END SO WITH THAT B EING SAID WHAT SHOULD I BE LOOKING FOR THAT WILL BOLT IN WITHOUT ANY FAB HAVE ACCESS TO A 10 BOLT OUT OF A 71 CHEVELLE WILL THIS FIT APPRECIATE ALL ADVISE

 

[MrSony]

Your rear most likely has 3.42 gears, not 3.43 and while its generally not recommended you can put some power through the gbody 7.5s, but its not worth the risk even if you go all out and build them up. A 10 bolt from a 68-72 CHEVROLET a body like s Malibu/chevelle will fit but you will need custom upper and lower control arms because that rear end is about an inch or so wider on either side. UMI makes upper and lower arms that are adjustable and have heim joints to avoid binding. If you wanna keep it gm but want it to be bullet proof, get a 12 bolt from a 68-72 CHEVELLE. The BOP rear ends are different and won't fit. In short, that 10 bolt chevelle rear will work, just rebuild it first. Gears, axles, new posi unit, gaskets, bearings, etc.

 

[MrSony]

Forgot to add, may need to move the spring perches on the chevelle rear end as it is wider. Not a deal breaker IMO. Any competent machine or metal shop can reweld them wherever you need them.

 

[565bbchevy]

If it's within your budget I personally would go for the 9" if you plan on racing it, since there are many manufacturers that sell them and they are a true bolt in requiring no special suspension parts or modification to the rear end itself plus you can get them in factory width that will not affect how your current rims fit on the back of your car.
Also with a 9" you are dealing with a brand new housing that is properly strengthened instead of a 40+ year old housing that has been through who knows what.
And there is the added benefit of having a third member that drops out that makes gear changes so much easier.

 

[Qdub24]

I love the GN 8.5" I put in my Cutlass w/posi and 3.42; direct bolt in, just had to shorten the DS about an inch. Looking for another to put in my Elco. Mine cost about half the price of a well built Ford 9" and hasn't given me any problems.

 

[LS WAGON]

I used a Ford 8.8 out of the fox body Mustang. It was a 3.73 posi already and changed the axles to 5 lug. But as Mr Sony has mentioned it is recommended to use aftermarket upper & lower control arms. The only fabrication needed was welding on the spring perches and a driveshaft.

 

[bubbameano]

I put a Currie G-Body 9 " with Dick Miller Racing adjustable control arms that I got for $500 in my 83 camino

 

[Bigdaddydupree]

8.5 is a good option as others have said. I personally have a moser m9 in my car and the reason is because I have broke an axle before. Word to the wise is run decent axles and c clip eliminators, your quarter panels will thank you later.

 

[Bigdaddydupree]

I had c clip eliminators on my 8.5 and never had a leak. But I sold it and now have a 9".

 

[565bbchevy]

While I feel an 8.5 will work for many applications it also has it's limitations besides the fact there are only so many available and many people now think they are made of gold and price accordingly so if you plan on making enough power to require an aftermarket differential carrier, new gears and upgraded axles then basically all you are using is the housing and I think starting off with a 9" housing that is stronger and already has upgraded axles and does not require c-clip eliminators to be track legal puts you ahead at this point.
But this only applies if you require that much rear end to handle the power.